Systems including one or more sun sensors for determining the angle of incidence of solar radiation are used for orienting satellites or solar generators mounted thereon relative to the sun, among other applications. According to a basic principle of one type of such sun sensor system, the system includes an arrangement of a plurality of light sensitive elements, i.e. a photosensitive detector array, and a shadow mask having a transparent region and an opaque or non-transparent region arranged at a certain spacing in front of the photosensitive elements, in the radiation beam path of the radiation source, and particularly the sun. One or more of the photosensitive elements are thereby shadowed or shaded by the shadow mask, dependent on the particular angle of incidence of the solar radiation. By evaluating the output signals provided by the photosensitive elements, the system generates a final output signal corresponding to the angle of incidence of the solar radiation, i.e. the angle of the sun relative to the sun sensor.
As an example, one type of known sun sensor has a shadow mask configured as a slit diaphragm or aperture, whereby the approximately parallel sunlight passes through the slit aperture onto the photodetector array. In such an arrangement, the position of the projection of the slit aperture, i.e. the position at which the line of sunlight passing through the slit aperture falls onto the photosensitive elements, will vary depending on the solar incidence angle. As a result, the location at which a photocurrent is generated on the photodetector array will also vary, and can thus be evaluated to determine the solar incidence angle.
U.S. Pat. No. 4,999,483 (Okamoto) discloses a sun sensor in which the photodetector array is a linear array or arrangement of a plurality of light sensitive elements, and particularly a plurality of photodiodes, arranged one after another along a line in a first linear direction. A shielding element or shadow mask arranged at a spacing in front of the arrangement of light sensitive elements has an opening in the shape of a triangle therein, whereby one side edge of the triangle extends perpendicularly to the first linear direction, another side edge is oriented at a sloping angle relative to the first side edge, and the third side edge interconnects the two above-mentioned side edges and extends parallel to the first linear direction. With this arrangement, the incident sunlight passing through the triangular opening falls on and illuminates a plurality of the photodiodes in an illuminated region bounded by the second and third side edges of the triangular opening. The position of the group of illuminated photodiodes along the linear photodetector array is dependent on the angle of incidence of the sunlight in a plane parallel to the first linear direction, while the number of illuminated photodiodes is dependent on the angle of incidence of the sunlight in a plane perpendicular to the first linear direction. The entirety of the disclosure of U.S. Pat. No. 4,999,483 is incorporated herein by reference, because a person of ordinary skill will recognize that some of the components of the system disclosed therein can be used in the present inventive system as well.
U.S. Pat. No. 5,264,691 (Hegyi) discloses a system including a photosensor that comprises an arrangement or array of four quadrilateral light sensitive elements of equal size or surface area and a shadow mask arranged at a spacing in front of the light sensitive elements in the light beam path of the light source. The shadow mask has a quadrilateral opening therein, of which the side edges respectively extend parallel to the side edges of the array of light sensitive elements. Thus, when sunlight falls on the photosensor in a normal direction, i.e. perpendicularly in two dimensions, then the light passes through the quadrilateral opening in the shadow mask and falls uniformly onto each one of the light sensitive elements of the photodetector array. In this situation, each one of the light sensitive elements outputs an equivalent photocurrent. When the angle of incidence of the sunlight changes, the projected image of the quadrilateral opening of the shadow mask will correspondingly move across the photodetector array, whereby at least a portion of one or more of the light sensitive elements will become shaded, and accordingly this particular light sensitive element will output a reduced photocurrent. With this arrangement, the angle of incidence of the sunlight in two directions relative to the photodetector array can be determined by evaluating the ratios or relationships of the respective photocurrent levels output by the respective light sensitive elements. The entirety of the disclosure of U.S. Pat. No. 5,264,691 is incorporated herein by reference, because a person of ordinary skill will recognize that some of the components of the system disclosed therein can be used in the present inventive system as well.
The known sun sensor arrangements, including those described above, suffer several disadvantages. Foremost is a lack of sufficient precision in the determination of the incidence angle. Generally, the precision of the determination is limited by the effective pixel size of the light sensitive elements. Alternatively, complex structural arrangements or complex circuit arrangements are necessary for achieving a greater precision. Such arrangements are more expensive and complicated to manufacture, and more difficult and complicated to operate reliably.